The Agriculture Department in 2004 gave the green light to using carbon monoxide gas to keep older cuts of meat looking red and fresh, even though scientists at the two companies promoting the technology had questioned the validity of their own safety tests, congressional investigators revealed yesterday.

The tests, conducted by Cargill and Hormel Foods, both of Minnesota, were part of a joint effort to persuade federal regulators to allow use of the gas without going through a public approval process. Inexplicably, however, the tests found that microbial counts on meat that had been left under-refrigerated went down over time instead of up, as expected, even as other indicators of spoilage increased, suggesting the possibility of some kind of error.

"Believe me, we are also puzzled by the data," a Hormel employee wrote in a May 2004 e-mail, marked CONFIDENTIAL, to a colleague at Cargill. "Please let me know if you see any other funny data . . ." he wrote later. "Quite honestly, this test seemed to raise more questions than what it answered."

Yet Agriculture Department scientists did not question the data when they reviewed them a few weeks later, and then relied upon them to reverse the agency's earlier decision to oppose the technology, Rep. Bart Stupak (D-Mich.), chairman of the House Energy and Commerce subcommittee on oversight and investigations, said at a hearing. In July 2004, acting on USDA's recommendation, the Food and Drug Administration gave the technology final approval.

Asked by Stupak if the e-mails raise concerns about the approval, the Agriculture Department's lead reviewer, Robert Post, said: "Based on this information, I think this leads to some questions, yes."

In another surprise at yesterday's hearing, the chief executives of Cargill and Hormel said for the first time that their companies are willing to put labels on their carbon monoxide-treated meats that would say, "Color is not an accurate indicator of freshness."

That concession, made before a combative Stupak and other lawmakers, was the latest victory for those who oppose use of the gas on meat and say that consumers are being deceived into thinking meat is fresher than it is. Packages of ground beef more than two years old were on display at the hearing looking red and fresh.

Giant Food, Stop & Shop and Safeway stores recently announced they would no longer sell the gassed meats. Tyson Foods, the nation's largest processor of meat and poultry, has said it will stop using the technology. And On Friday, Target stores asked the Agriculture Department for permission to use labels that would say: "Carbon monoxide has been used to preserve the color of this product. Do not rely on color or the 'use or freeze by' date alone to judge the freshness of the product."

Whether those disclaimers will be deemed adequate by opponents -- or acceptable to the Agriculture Department, which regulates food labels and has said it is reconsidering the science behind the gas treatment -- remained unclear yesterday.

Industry officials, who have complained that they lose $1 billion in sales every year from having to toss or discount meat that is still edible but does not look red and appetizing, defended the gas, which locks in red color indefinitely.

"We're very comfortable with the science surrounding this packaging," said Gregory Page, Cargill's chief executive, noting that the company has received 48 complaints of "off" meat out of 23 million packages sold -- every one of which has the company's toll-free telephone number.

Stupak responded by asking Hormel's chief executive, Jeffrey Ettinger, to read the phone number on a package at the hearing, something Ettinger could not do because, he said, the type is too small.

FDA officials at the hearing stood by their decision to categorize the gas as "generally recognized as safe," or GRAS, for use on red meat and tuna -- a category that allows companies to bypass a public regulatory review.

"This particular issue is not a safety concern that is even a remote concern on our radar," said David Acheson, FDA's assistant commissioner for food protection, adding that the agency is nonetheless conducting a full review in response to a citizen petition.

Ranking subcommittee member Edward Whitfield (R-Ky.) and others noted that the petition was filed by a company from Stupak's home state, a meat-treatment business threatened by carbon monoxide use. Congress should not get dragged into an "intra-industry" fight under the guise of consumer protection, said Rep. Marsha Blackburn (R-Tenn.).

Opponents have said GRAS status is inappropriate for a technology banned by the European Union, Japan and Canada.

Phil Minerich, a Hormel scientist who reviewed the tests that produced the confusing results, told the subcommittee that the decline in microbe levels was eventually interpreted to be "a good thing," suggesting the gas mixture might suppress bacterial growth.

But he said the company has not figured out why other evidence of bacterial growth, including gas production and increased odor, increased at the same time.